Allografts of the amebocyte producing organ (APO) from schistosome- resistant Biomphalaria glabrata snails confer resistance to a subsequent challenge with the human pathogen Schistosoma mansoni in susceptible snails. However, the mechanism for this adaptive transfer of resistance, and at a more fundamental level the normal function of the APO, are not known. The working hypothesis for this proposal is that the transplanted APO produces phenotypically resistant hemocytes in the recipient snail, thereby forming a hemocyte chimera, and these resistant hemocytes than kill invading sporocysts. This hypothesis will be tested by examining recipient tissues for donor polymorphisms with the use of RAPD-PCR. This technique will also allow description of the time course of infiltration of donor cells into the recipient's hemolymph, and will provide insights on hemocyte lifespan. With the use of fluorescently labeled probes, identity of hemocytes in granulomas surrounding killed sporocysts in snails with transferred resistance. Finally, an alternative hypothesis, that the APO confers resistance by secreting "resistance factors," will be tested by attempting to passively transfer resistance from snails with APO allografts by injecting their plasma into susceptible snails.